- O-Neill and Brennan
- Oasis Recruitment Group
- Oasis Recruitment Group
- ODS Group
- Off The Chain
- Offshore Recruitment Services
- OFO UK
- Oldfield Consulting
- Oldfield Ellis Associates
- Olympus Group
- Omega Resourcing Ltd
- One Stop Java Shop
- Online Business Systems
- Online e Group
- Options Employment (Midlands & West) Ltd